1. Field of Invention
This invention pertains to methods and devices for counting objects. More particularly, this invention pertains to methods and devices for counting objects in a stream of stacked or nested objects.
2. Description of the Related Art
Containers, container lids, plates, bowls, trays, cups, and other similar articles (hereinafter, collectively, “articles”) of the type having a circumferential rim and a depending concave body portion are common mass-produced goods. Such articles are often fabricated from a disposable or semi-disposable material such as paper, plastic, polystyrene, aluminum, or any of numerous other materials having the desired combination of strength, weight, and cost. It is common to fit, slide, stack, or otherwise nest the articles to facilitate the automated, and often high speed, handling of large volumes of articles achieved by modern production methods. The handling of nested articles includes the counting of the articles necessary to separate a selected number of articles from the stream of nested articles into a group for packaging and distribution.
Conventional article counting techniques used in the production and packaging of nested articles are prone to produce groups of articles exhibiting more or fewer than the desired number of articles. Inaccurate counts result in economic harm to the article producer when the package contains more than the stated number of articles and economic harm to the article consumer (and potentially a loss of goodwill to the article producer) when the package contains fewer than the stated number of articles.
One conventional technique “counts” the nested articles based on the overall length of the nested dimension of the stack. This technique requires a high degree of uniformity in the number of articles per unit length of the article stream (hereinafter, the “stacking density”) in order to be successful in providing an accurate and reliable count of nested articles in the stream. Because the articles to be counted often exhibit variations in stacking density along the continuous stream of nested articles, the actual number of articles in a group often varies from the desired number of articles.
Another conventional technique counts the individual articles in the article stream using optical or mechanical sensors to detect the individual articles as the stream of articles passes the sensor. FIG. 1 illustrates one version of a conventional device counting individual articles using an optical sensor. In FIG. 1, a photoemitter 1 is positioned along the path of the article stream and directs a beam of light 2 to a photoreceiver 3 along a line tangent to the article stream. As the articles move past the photoemitter/photoreceiver pair, the rims 30 interrupt the beam 2. The output of the photoreceiver 3 is by a logical unit, such as a controller, processor, or computer that records the passage of an article each time the beam 2 is interrupted. This technique relies on adequate separation between adjacent rims in the article stream, and a high degree of precision in the positioning of the sensor relative to the article stream, and a high degree of uniformity in the size and shape of the articles. It is not uncommon for these conditions to fail to occur, causing an inaccurate count the number of articles.